Heart disease, specifically coronary artery disease, is a major cause of death, disability, and healthcare expense in the United States and other industrialized countries. A number of methods and devices for treating coronary artery disease have been developed, some of which are specifically designed to treat the complications resulting from atherosclerosis and other forms of coronary arterial narrowing.
One method for treating such vascular conditions is percutaneous transluminal coronary angioplasty (PTCA). During PTCA, a balloon catheter device is inflated to dilate a stenotic blood vessel. The stenosis may be the result of a lesion such as a plaque or thrombus. When inflated, the pressurized balloon exerts a compressive force on the lesion, thereby increasing the inner diameter of the affected vessel. The increased interior vessel diameter facilitates improved blood flow.
However, soon after the procedure, a significant proportion of treated vessels restenose. Various methods have been developed to prevent or inhibit this restenosis. One method is to provide a physical support in the form of a stent to maintain the increased interior diameter of the vessel lumen.
Stents are generally cylindrical shaped devices that are radially expandable to hold open a segment of a vessel or other anatomical lumen after implantation into the body lumen. Various types of stents are in use, including expandable and self-expanding stents. Expandable stents generally are conveyed to the area to be treated on balloon catheters or other expandable devices. For insertion, the stent is positioned in a compressed configuration along the delivery device, for example crimped onto a balloon that is folded or otherwise wrapped about a guide wire that is part of the delivery device. After the stent is positioned across the lesion, it is expanded by the delivery device, causing the diameter to expand. For a self-expanding stent, commonly a sheath is retracted, allowing expansion of the stent.
The stent acts as a scaffold to support the lumen in an open position. Configurations of stents include a cylindrical tube defined by a mesh, interconnected stents, or like segments. Exemplary stents are disclosed in U.S. Pat. No. 5,292,331 to Boneau, U.S. Pat. No. 6,090,127 to Globerman, U.S. Pat. No. 5,133,732 to Wiktor, U.S. Pat. No. 4,739,762 to Palmaz, and U.S. Pat. No. 5,421,955 to Lau.
Stents have been used with coatings to deliver drugs or other therapeutic agents at the site of the stent to assist in preventing inflammation, infection, thrombosis, and proliferation of cell growth that can occlude the vessel lumen. However, the coated stent can deliver drugs to only those portions of the vessel in contact with the stent. Because restenosis is often a greater problem in tissue adjacent to the ends of a stent than it is elsewhere along the stent, drug delivery using the stent alone may not be fully effective.
Vascular delivery of drugs and other agents intended to inhibit restenosis has also been accomplished using devices that inject or otherwise infuse the agents into the treated portion of the vessel before, during, or after performing PTCA. Unlike coated stents, these devices deliver the anti-restenosis agents without additionally providing physical support for the treated vessel.
One such device is disclosed in U.S. patent application Publication No. 2003/0055446 to Seward and Pisano. This device includes an actuator joined to a distal end of a catheter. The actuator has an expandable section designed to deploy a needle. When the expandable section is in an unactuated, furled condition, the needle is enclosed within the folds of the expandable section, preventing the needle from injuring the vessel walls while the catheter is being introduced into the target area of a vessel. Fluid connections are provided to supply a therapeutic or diagnostic agent to the needle and to provide an activating fluid to the actuator. When actuated, the expandable section unfurls and expands, thrusting the needle outward, penetrating the vessel wall and delivering the agent. When the activating fluid is removed, the expandable section returns to a furled state with the needle again enclosed within the folds of the expandable section for removal of the catheter from the vessel.
Another device for vascular delivery of therapeutic agents is disclosed in U.S. Pat. No. 5,681,281 to Vigil and Barath. In one embodiment, the device includes an inflatable balloon mounted on a catheter. A tubular sheath surrounds a substantial portion of the inflatable balloon, and a plurality of injectors is mounted on the sleeve. In another embodiment, a plurality of tubular fluid passageways is mounted on the balloon, extending longitudinally across the balloon, and a plurality of injectors is mounted on each fluid passageway. In both embodiments, inflation of the balloon embeds the injectors in a vessel wall, and a medication is delivered through the injectors into the vessel wall.
Still another device for delivering drugs to a vessel is disclosed in U.S. Pat. No. 6,283,951 to Flaherty et al. The device includes a catheter, an orientation element in a predetermined relationship with the periphery of the catheter, a drug delivery element, and in some embodiments a puncturing element and/or an imaging element. In one embodiment, the drug delivery element is an osmotic surface on the catheter. In another embodiment, a puncturing element, for example a needle, is deployed through an opening in a distal portion of the catheter. The drug delivery element, in this example a lumen within the needle, delivers a drug to the tissue. The drug delivery element may include electrodes that, when current is passed between the electrodes, direct a fluid ionophoretically.
Thus, coated stents support the lumen of a vessel in an open position following PTCA but may be limited in their ability to deliver an anti-restenosis agent to the wall of the treated vessel. Injection devices, on the other hand, offer flexibility in delivery of an anti-restenosis agent do not provide scaffolding to maintain the increase in the interior diameter of a vessel lumen that has been achieved by performing PTCA. Therefore, it would be desirable to have a system and method for treating a vascular condition that overcome the aforementioned and other disadvantages.